Base stations are used in the transfer of telephone calls along a cellular telephone system or network. Each base station has a backplane or plate. The backplane is a printed circuit board with two or more connectors mounted on the board. Circuit card assemblies, each of which has a circuit card and a circuit card connector on the circuit card, are attached to the backplane with the circuit card connectors each coupled to one of the backplane connectors so that the circuit cards can interface with each other through the backplane. The backplane and circuit cards are contained in a sheet metal enclosure known in the industry as a rack.
The circuitry of the base station is commonly cooled to operate reliably. One way in which the circuitry may be cooled is to circulate the air in the rack through an air conditioner or heat exchanger. The use of an air conditioner or heat exchanger is not universally desirable. The air conditioner or heat exchanger may make the overall base station construction complex, leading potentially to frequent and/or costly maintenance. The air conditioner or heat exchanger may also add significantly to the cost of manufacturing the base station. Moreover, the air conditioner or heat exchanger may raise the power consumption of the base station to an undesirable level.
Alternatively, the circuitry may be cooled using air drawn through the base station from the surrounding environment. This arrangement can also create problems. If the air is polluted, soot and other contaminants in the air can degrade the performance of the circuitry. For optimum performance, it is important to prevent pollution from reaching the connection sites between the backplane and the circuit card.